Drive devices for a travel assembly are used in travel assemblies for an optical system of an image read scanner, a printer head, etc. Normally, a travel assembly has a driver side driven by a driving rope at one side and a follower side following the driver side at the other side when viewed from a travel direction. The driver side is supported by two bearings spaced along the travel direction, and the follower side is supported by one bearing. Therefore, each time the travel assembly starts or stops, the follower side cannot follow the start or stop movement because of bearing play of the driver side, resulting in its delayed movement, which may cause loss of reading or twice reading in reading an original and, with a mirror travel assembly in a copying machine, may cause irregular movements, thus introducing jittering in the travel direction.
On the other hand, a drive device for an optical scan system has been proposed for a copying machine which intends to eliminate the aforesaid drawback by applying driving forces to both sides of a travel assembly. This proposal, however, necessitates a longer wire rope because both sides share the rope, which results in a larger diameter of rope and a stronger spring in use for applying tension, thus causing complicated construction of drive device.
Furthermore, a wire-type drive device has been well known for a travel assembly in which driving forces are applied on both sides of a travel assembly in the same way as above described, but the aforesaid long wire rope is divided into two short separate ropes to drive respectively both sides of a travel assembly. Engaged with either side of a travel assembly through an independent tension spring which tends to expand and contract depending on forces applied in scan movements of the travel assembly, each wire rope causes irregular motion of the travel assembly.